Hard faced plastic armor



June 23, 1970 R. L.. COOK 3,516,893

` HARDA FACED PLAsIc ARMOR 'Y Filed June 23, 1966 /l/l l,

arr/'M556 United Statesl Patent Office 3,516,898 Patented June 23, 1970US. Cl. 161-93 5 Claims ABSTRACT F THE DISCLOSURE A hard faced plasticarmor plate laminate is provided which can be either clear or opaque.The facing layer is laminated to a base by a flexible adhesive. Thefacing layer is a very hard material taken from a group includingalumina ceramic, boron carbide ceramic, and silicon carbide ceramic. Thebase is preferably a resin impregnated glass fabric that tends todelaminate with a force absorbing action over a wide area upon impact.

This invention relates to hard faced plastic armor plate laminate, and,more particularly, to a laminate structure which can be either clear oropaque, which is highly resistant to armor piercing type of bullets, andit is a continuation-in-part and an improvement over patent applicationNo. 268,765, field Mar. 28, 1963, and also assigned to GoodyearAerospace Corporation, Akron, Ohio.

Heretofore it has been known that there are many and varied ways tocreate armored plate. However, this armored plate has usually beenmetal, which has been heavy and expensive. There has been attempts tocreate transparent bullet resisting armored plates, but these plateshave also had to be extremely thick and heavy as well as expensive, andhave not proved practical or durable for use in military warfare, ormore particularly for use in aircraft where lightness of weight is anessential criteria.

It is the general object of the invention to avoid and overcome theforegoing and other difliculties of and objections to prior artpractices by the provisions of a hard faced plastic armo-r platelaminate structure which is highly effective to bullet resistance,extremely light in weight and easy to handle, and which is alsorelatively low in cost.

Another object of the invention is the provision of an armor plate madeof ceramic and plastic wherein the ceramic is positioned to shatter or,by fusion and melting to dissipate the bullet and to then carry the loadof impact into a resilient backing, thereby distributing the force ofthe bullet over a large diameter on the final load carrying plasticlayer.

Another object of the invention is to provide a lightweight, effectiveshaped charge resistant plastic laminate utilizing the principle of abrittle outer layer which, by breaking up in a conical pattern tends todissipate the jet blast of a shaped charge in combination with the lowthermal conductivity and high heat of ablation properties of a plasticbacking layer.

Another object of the invention is to provide a plastic laminatearmorplate utilizing a very hard aluminum oxide as an outer layer withthe layer segmented into tiles so that the concentrated energy of aprojectile can be locally absorbed without fracture and loss of thesurrounding facings, the substrata layer being bonded to the aluminumoxide layer by a flexible bonding agent capable of retaining the tileunder severe impact deformation.

Another object of the invention is to provide a laminate of the type setforth in which the substrata yields and de'laminates to absorb forceduring bullet penetration.

The aforesaid objects of the invention, and other objects which willbecome apparent as the description proceeds, are achieved by providing alaminate structure resistant to either a solid steel core projectile ora shaped charge projectile and including the combination of a facinglayer made from an extremely hard material, a reinforced plasticsubstrata layer, flexible bonding means between the facing layer and thesubstrata layer, the facing layer being segmented into sections so thatthe concentrated energy of the projectile can be locally absorbedwithout fracture and loss of the surrounding facing, the facing layerhaving the tendency to shatter in an expanding conical shape inwardlyfrom the impact point of the bullet, the substrata layer having lowthermal conductivity and high heat ablation properties, and thesubstrata having high resilience and high impact resistance.

For a better understanding of the invention reference should be had tothe accompanying drawings, wherein:

FIG. l is a fragmentary cross sectional view of a laminate structurecomprising one embodiment of the invention;

FIG. 2 is a fragmentary cross sectional view of the laminate structureof FIG. l showing a projectile just after striking the outer layer ofthe laminate and the fragmentation that results therefrom;

FIG. 3A is a fragmentary cross sectional view of a transparent form ofthe plastic laminate armor plate comprising the invention;

FIG. 3B is a fragmentary cross sectional view of a laminate structurewith a hard outer layer and a metallic backing layer; and

FIG. 4 is a view similar to FIG. 2 but illustrating the fartherpenetration of the projectile.

With a specific reference to the form of the invention illustrated inFIGS. l and 2 of the drawings, the numeral 1 indicates generally aplastic laminate armour plate comprising a plastic substrata layer 2reinforced with glass fabric 2A, an extremely hard surface layer 3, andwith the layers 2 and 3 being bonded together by a flexible bondingagent 4. lIn order to prevent spalling or flaking of the outer layer 3upon projectile impact, a thin flexible rubberized layer or sheet 5 ispreferably provided over the outer layer 3. The sheet 5 may also be ofballastic nylon cloth or felt or resin impregnated glass fabric tofurther prevent fragmentation of ceramic layer 3.

The first principle of the invention is that the outer layer 3 must beof an extremely hard material in order to blunt, melt or shatter theoncoming projectiles. After extensive testing, it was found that amaterial such as aluminum oxide or an alumina tile or alumina ceramicproved to have the lightweight characteristics desired, yet provided theextremely hard surface necessary to achieve the blunting or shatteringof the projectiles upon impact. Preferably a ceramic having a highalumina content is employed, for example or more, and preferably overExcellent results have been obtained with an alumina content of 94% Thealumina faced composite armor has a weight advantage of approximately 2to l over aluminum armor, as well'as providing better armor piercingprotection. Through extensive testing, it was found that a thickness ofthe layer 3 between 1A inch to 3/8 of an inch, and in the combinationabove described, provided adequate armor piercing protection for 30.06armor piercing ammunition at 5 yard shooting range and 0 degreeObliquity. Armor protection of this type is desired for aircraft andhelicopter protection against ground troop fire. Comparing the aluminaceramic faced and plastic body reinforced armor plate of the present 3invention with steel shows a weight penetration advantage for thealumina ceramic over steel of about 4 to 1.

At least certain other very hard lightweight materials can be used tomeet the objects of the invention. These would include silicon carbideceramic and boron carbide ceramic, also of high density and purity. Forexample, HD form carbide and KT silicon carbide by the CarborundumCompany of Niagara Falls, N.Y. having boron carbide contents of betweenabout 75 to 85 percent and silicon carbide content of about 97%respectively will meet the objects of the invention. Since the boroncarbide and silicon carbide are somewhat lighter in specific gravitythan the alumina ceramic layers of these materials will have to be alittle thicker to achieve the same projectile defeating properties. But,it has been found that the overall weight of the armor using boroncarbide or silicon carbide as compared to alumina ceramic will be aboutthe same.

It is to be particularly noted, with respect to FIG. 2, that the ceramiclayer 3 tends to fracture in an expanding conical shape, indicatedgenerally by the numeral 6, from the point of impact created by theprojectile 7. The angle of conical fracture is believed to correspond tothe shock wave sent ahead of the projectile. The conical expansion 6 ofthe impact area greatly distributes the rather small and compact impactforce of the projectile 7 over a much larger area onto the substratalayer 2. Also, it was found to be advantageous to form the layer 3 in aplurality of smaller tiles indicated at `8, which tend to localize theshattering, and which sections can be easily replaced to make the armorlaminate plate usable for a long service life, even after it hasabsorbed the impact of many projectiles. During testing it was foundthat if a projectile 7 impacted upon the gaps 9 between tiles 8, thatthe armor protection properties were just as good as if the projectile 7hit towards the center of a tile, as indicated in FIG. 2.

The second principle of the armor laminate plate construction is basedon the low thermal conductivity and high heat of ablation of plastics,plus the resilience and high impact resistance of the reinforced plasticsubstrata layer 2, and its force absorbing action by delaminating uponbullet impact. The layer 2 is made up of a plurality of layers of glassfabric, each layer formed of straight warp cords or filaments andundulating weft cords each of about the same strength. The layers may belaid in any random relation to each other, and in fact more than onelayer can be in the same direction. The layers are saturated with a lowcontent of resin and built up to a required thickness, for example,one-half inch. By leaving the original oils, resins, or dirt on theglass fabric caused by weaving and by using a low content of bindingresin, such as 25% of resin to 75% by weight of glass fabric a structureis provided in which the layers separate from cach other, or delaminate,with a force absorbing action upon being struck with a projectile.Typical binder resins are known polyester and phenolic resins.

The delaminating effect of the several layers upon projectile impact isshown in FIG. 4. The projectile 7, somewhat more shattered or flattened,has penetrated farther into the laminate. The conical plug 6 has movedagainst the substrata 2 to deiiect it downwardly over a relatively largearea. This causes delamination of the reinforcing layers in regions 14,and breakage at of some of the reinforcing layers of glass fabric. Theresult is a high force absorbing and smothering action upon theprojectile providing the protection desired.

However, results have also indicated that at least certain of the forceabsorbing characteristics or delaminating effects are achieved by theuse of a metallic backing plate such as 12A indicated in FIG. 3B. It hasbeen found that either aluminum or steel plate will meet these desiredobjects. Suitable forms would include aluminum alloys identified byalloy and temper from a group which might include 2024-0, 2024-T3, M-T4,5083-0, and 5083- H113, and steel in sheet from where differentcombinations of cold rolling, annealing, piercing, and leveling may beused depending upon the desired tension, compression, and ultimate yieldlevels desired for each particular' armor application. Naturally, thearmor requirements for each particular use will vary, and so theproperties of the metallic backing sheet must vary.

The fiexible bonding agent 4 is preferably an elastomeric material whichis polymerizable at room temperature and containing 100% solids when inliquid form, for example, a polysulphide or silicone rubber adhesive.

Therefore, the principles of the invention are two fold:

(l) To blunt and shatter oncoming projectiles by the hard and brittlefacings of alumina ceramic, boron carbide or silicon carbide.

(2) To dissipate the kinetic energy of the projectile by lowconductivity, high heat ablation, delamination, elasticity, and impactresistance in a reinforced plastic substrata layer, or a suitable steelor aluminum backing plate,

These actions are achieved both against solid steel core projectiles andagainst shaped charge projectiles. In the case of the steel coreprojectiles the core appears usually to fracture and/or melt evendisappearing in part due apparently to gasifying. ln the case of shapedcharge projectiles the discharged gas is dissipated over and around thecone and delaminate over a large area to largely lose its effectiveness.The ablative properties of the hard facing layers and the plastic metalbacking are thought to cause them to char and to set up cool gaseousboundary layers to prevent the hot gases of a shaped charge from burningthrough.

The embodiment of the invention illustrated in FIGS. l, 3B, and 4produces opaque armor plate. FIG. 3A illustrates a transparent armorplate, indicated generally by the numeral 1f? and comprising an outerlayer l1 secured to a substrata layer 12 by a flexible bonding layer 13.In exhaustive testing it was fo-und that plain window glass of between/s inch to 3A; inch thickness provides a hard surface layer 11approaching the results of the alumina ceramic tile in the alreadydescribed embodiment of the invention. The substrata layer 12 is a clearplastic material, for example, stretched methyl methacrylate, having ahigh degree of toughness. Tests were also conducted on full temperedglass plate, 1/4 inch thick, and it was found that the tempered glass,although perhaps harder than the common window glass, tended to shatterso much more than the window glass that it completely obliterated visionthrough the armored plate, whereas the common window glass tended toshatter only around a small portion of the periphery of the impact area.

The transparent armor plate of the invention is not as effective as theopaque and must normally be made thicker, but has the transparentfeature which is sometimes a requisite.

The adhesive layer 13 must also be transparent and is usually a methylmethacrylate cement.

FIG. 3B illustrates an embodiment of the invention having a continuoushard facing layer 11A. Naturally, it is easier and cheaper to form thefacing layer 11A in a continuous sheet and in at least some instancesthis may be the best solution. However, it should be recognized that thecontinuous sheet will not localize shattering as well as the separatetile-like configurations of FIGS. 1, 2, and 4.

While in accordance with the patent statutes one best known embodimentof the invention has been illustrated and described in detail, it is tobe particularly understood that the invention is not limited thereto orthereby, but that the inventive scope is defined in the appended claims.

What is claimed is:

1. Armor plate including a base having a plurality of layers of resinimpregnated glass fabric, the weight of the resin in the base beingbetween 15% to 35% and the weight of the glass fabric being between to85% so that the layers of glass fabric delaminate with a force absorbingaction in stopping a projectile, a continuous facing layer on the baseconsisting of a very hard material from the group including boroncarbide ceramic, and silicon carbide ceramic, each of said materialshaving the characteristic of shattering and deforming a projectilestriking it and of forming a conical plug of increasing diameter in thedirection of projectile penetration to distribute the force of theprojectile over a greater area of the base, and a layer of flexibleadhesive securing the facing layer to the base.

2. Armor plate according to claim 1 wherein the group of very hardmaterials the boron carbide ceramic has a boron carbide content of over85%, and the silicon carbide ceramic has a silicon carbide content ofover 95%.

3. Armor plate according to claim 1 where the facing layer is brokeninto a plurality of separate tiles in very close spaced relation tolocalize shattering caused by the impact of a projectile.

4. Armor plate including a base made from a metallic plate having greatresilient qualities, tensile strength and stretchability to withstandthe impact of a projectile with a force absorbing action, a continuousfacing layer on the base consisting of a very hard material from thegroup including alumina ceramic, boron carbide ceramic, and siliconcarbide ceramic, each of said materials having the characteristic ofshattering and deforming a projectile striking it and of forming aconical plug of increasing diameter in the direction of projectilepenetration to distribute the force of the projectile over a greaterarea of the base, and a layer of flexible adhesive securing the facinglayer to the base.

5. Armor plate according to claim 4 wherein the group of very hardmaterials the alumina ceramic has an alumina content of over the boroncarbide ceramic has a boron carbide content of over and the siliconcarbide ceramic has a silicon carbide content of over i References CitedUNITED STATES PATENTS 2,234,829 3/1911 Neher et al. 161-204 2,733,1771/1956 Meyer 161-404 2,778,761 1/1957 Frieder et al v 161-404 2,861,02111/1958 Dietz et al. 161-404 2,991,209 7/ 1961 Warrall 161-404` CARL D.QUARFORTH, Primary Examiner H. E. BEHREND, Assistant Examiner U.S. C1.X.R. 161-36, 204

Disclaimer and Dedication 3,516,898.Rchard L. Cook, Phoenix, Ariz. HARDFACED PLASTIC AR- MOR. Patent dated June 23, 1970. Disclaimer andDedication filed Oct. 14, 1983, by the assignee, Goodyear AerospaceCorp. Hereby disclaims and dedicates to the Public the term of thispatent subsequent to Aug. 8, 1983.

[Official Gazette December 20, 1983.]

